Motor vehicles such as motor cars are prone to theft. Many different systems have, therefore, been proposed to make motor vehicles more secure from theft. One popular approach is to use an engine immobilizer, which is a discrete device which cuts electrical power to essential components, such as a fuel pump, an engine control unit (ECU), or spark plugs, if a security device is not deactivated when a person enters the car. Many immobilizers, however, can be bypassed to restore power.
Another approach is to incorporate the functions of the immobilizer in the ECU, and to incorporate associated electronic circuitry in a fuel pump. The fuel pump circuitry has to receive a data signal from the ECU in order to activate the fuel pump to respond to control signals from the ECU. In this way, even if the ECU is bypassed to provide power to the fuel pump, the fuel pump will not work unless it has already received a valid activation code from the engine control unit. This improves security against vehicle theft, but unfortunately, if a thief knows the correct activation code for the fuel pump, the data line from the ECU to the pump can be bypassed, and a valid activation code supplied directly to the fuel pump. It is, therefore, possible for a thief to defeat such a vehicle security system.